1. Field of the Invention
The present invention relates to optical transmission and receiver modules for use in optical communication. In particular, the present invention relates to an optical transmission and receiver module suitable for single-fiber bi-directional communication.
2. Description of the Related Art
An optical transmission and receiver module of the related art includes first and second packages accommodating a light emitting device and a light receiving device, respectively, and a third package accommodating an optical filter. The first and second packages includes a lens for a light-emitting device and a lens for a light-receiving device, respectively. Accordingly, the optical transmission and receiver module of the related art has many parts.
The optical transmission and receiver module of the related art is structured such that light from the light emitting device passes through the light-emitting-device lens and is incident on an optical fiber after passing through the optical filter, and light emitted from the optical fiber passes through the optical filter and is led to the light receiving device after passing through the light-receiving-device lens. In other words, the optical filter is disposed between the optical fiber and each lens. A specific example is described below.
FIG. 5 is a side sectional view showing a schematic section of a conventional optical transmission and receiver module 100. The optical transmission and receiver module 100 includes a laser diode 101 for emitting light which is to be incident on an optical fiber 200, a photodiode 102 for receiving light output from the optical fiber 200, and an optical filter 103 which allows the light from the laser diode 101 to pass through it and which reflects light to the photodiode 102 so as to changes the optical path. The laser diode 101 is mounted on a substrate 104 fixed to a package 105. The package 105 includes a lens 106 which opposes the laser diode 101 so that coupling between the light from the laser diode 101 and the optical fiber 200 is efficiently established. The photodiode 102 is fixed to a package 107 which is different from the package 105. As in the case of the package 105, the package 107 also includes a lens 108 which opposes the photodiode 102 so that light is efficiently coupled with the photodiode 102. Both packages 105 and 107 are separately fixed to another package 109 in which the optical fiber 200 and the optical filter 103 are held.
In this arrangement, light emitted from the laser diode 101 is converged by the lens 106, passes through the filter 103, and is incident on the optical fiber 200. Also, light emitted from the optical fiber 200 is reflected by the filter 103 so as to change its optical path, passes through the lens 108, and is received by the photodiode 102. This type of optical transmission and receiver module is disclosed in, for example, U.S. Pat. No. 5,841,562.
The conventional optical transmission and receiver module has a large number of parts. Accordingly, the module has a limitation in the reduction of its size, and it takes time to assemble the module. This causes a problem in that it is difficult to reduce the required cost.
As shown in FIG. 5, in the optical transmission and receiver module 100, the laser diode 101 and the photodiode 102 are separately accommodated in the packages 105 and 107, and the packages 105 and 107, and the optical filter 103 are further accommodated in the package 109 so as to be integrated. Thus, the optical transmission and receiver module 100 has a large number of parts. The packages 105 and 107 also have large numbers of parts since both respectively include the lenses 106 and 108.
After the laser diode 101 is accommodated in the package 105 and the photodiode 102 is accommodated in the package 107, the packages 105 and 107 are fixed to the package 109. Therefore, this requires a large number of production steps, and may cause high cost of production. Accordingly, improvement in productivity and economical efficiency is expected to be achieved.
In addition, due to the above large numbers of parts, it is difficult to reduce the size of the optical transmission and receiver module. In order to increase the number of users of an optical communication network so that wider-spread use of the optical fiber communication is enhanced, a small optical transmission and receiver module which has a less number of parts and which can be easily assembled at a low cost must be developed.